The present application relates generally to the field of internal combustion engines. More specifically, the present application relates to air passages within internal combustion engines.
Typically an internal combustion engine includes an intake runner extending between the throttle and the combustion chamber of the engine. For example, the intake runner may be a pipe extending from a throttle plate of a carburetor to an intake valve of the combustion chamber. For overhead valve type engines, the intake runner extends through the cylinder head. However in other engine configurations, such as L-head engines, the intake runner may extend through the engine block.
For some overhead valve engines, the intake runner has a simple geometry and is integrally formed during casting of a single-piece cylinder head. In such engines, the intake runner extends inward from a side of the cylinder head, in a generally straight path, where the path then opens to the combustion chamber. The straight path geometry may be relatively simple to manufacture, but may also provide significant drag to air passing through the intake runner as the air turns to pass into the cylinder. Such drag would reduce the flow rate of the air, decreasing the efficiency of the engine.
In other overhead valve engines, the intake runner has a complex design intended to reduce drag. Expendable cores of salt or sand may be used during casting to form the complex design. In such engines, the complex design may improve engine efficiency, however use of the expendable cores adds complexity to the manufacturing process and consumes additional materials and resources.